Removing Client Devices from Association with a Wireless Access Point

ABSTRACT

A wireless access point that serves one or more wireless client devices in a wireless network determines that at least one particular client device that is associated to the wireless access point should not be associated to the wireless access point. The wireless access point transmits frames so that they are received at the particular client device with reduced strength so as to provoke the particular client device to transition from the wireless access point.

TECHNICAL FIELD

The present disclosure relates to wireless communications, such aswireless local area networks.

BACKGROUND

In wireless local area network (WLAN) deployments, “sticky” clients arethose clients that stay associated with an access point (AP) even thoughthere are one or more other APs with a better link quality available tothe client. When a client stays associated to an AP when it should not,this causes lower link quality, and also causes airtime usage for theclient to be longer than average airtime usage, thus wasting WLANairtime.

The reason for sticky client behavior is the diverse roaming algorithmsthat are implemented by different vendors of client devices. Thisbehavior could be due to a variety of factors including that the clientdevice does not search for beacons from APs other than the AP to whichit is associated unless the quality of the link reduces to a very lowlevel, that the client device tends to avoid disruption on activeconnections, and/or other factors.

In enterprise WLAN design and deployments, reducing the number of stickyclients is important to maintain overall network performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless network environment in which oneor more wireless access points are configured to perform one or moremethods to provoke a wireless client device to transition to a differentwireless access point.

FIG. 2 is a block diagram of a wireless access point device configuredto perform one or more methods to provoke a wireless client device totransition to a different wireless access point.

FIG. 3 is a flow chart generally depicting operations performed by awireless access point to transition a client device to a differentwireless access point.

FIG. 4 is a flow chart depicting operations for a first method performedby a wireless access point to transition a client device to a differentwireless access point.

FIG. 5. is a block diagram depicting the first method.

FIG. 6 is a diagram depicting the spatial nulling operations performedby a wireless access point in accordance with any of the methodspresented herein.

FIG. 7 is a diagram showing plots of simulation results for the spatialnulling operations.

FIG. 8 is a flow chart depicting operations for a second methodperformed by a wireless access point to transition a client device to adifferent wireless access point.

FIG. 9 is a block diagram depicting the second method.

FIG. 10 is a flow chart depicting operations for a third methodperformed by a wireless access point to transition a client device to adifferent wireless access point.

FIG. 11 is a block diagram depicting the third method.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

In one embodiment, a wireless access point that serves one or morewireless client devices in a wireless network determines that at leastone particular client device that is associated to the wireless accesspoint should not be associated to the wireless access point. Thewireless access point transmits frames so that they are received at theparticular client device with reduced strength so as to provoke theparticular client device to transition from the wireless access point.

Example Embodiments

Reference is first made to FIG. 1. FIG. 1 shows a network environment 10that supports wireless network capability, such as a Wi-Fi® wirelesslocal area network (WLAN). To this end, there are multiple wirelessaccess points (APs), two of which are shown as an example at referencenumerals 20(1) and 20(2). The APs 20(1) and 20(2) support WLANconnectivity for multiple wireless client devices (also called “clients”herein) shown at reference numerals 40(1)-40(5). It should be understoodthat FIG. 1 is only a simplified example. There may be numerous more (orless) clients in a real network deployment.

There is back-end infrastructure that is used for control and otherfunctions of the WLAN. Specifically, the APs 20(1) and 20(2) connect toa wired local area network 30 to which are also connected a WLANcontroller 50 and a mobility services server 60. The WLAN controller 50performs control functions for the APs 20(1) and 20(2) and clients40(1)-40(5) as described further hereinafter. In addition, and asdescribed in more detail hereinafter, the mobility services server 60performs, among other things, location functions to track the locationsof clients based on data gathered from signals received at multiple APs(or other wireless devices at fixed locations). The WLAN controller 50and mobility services server 60 may reside on the same physicalapparatus, or may be applications running on a data center. Thus, boththe WLAN controller 50 and mobility services server 60 are not requiredin order to performance the techniques presented herein.

FIG. 1 also shows that client 40(4) is associated to AP 20(1), but is“sticky” in that it should not be associated to AP 20(1) due to lowsignal-to-noise ratio (SNR) conditions for the wireless channel betweenAP 20(1) and client 40(4). However, client 40(4) is stuck to AP 20(1)because it does not scan (passively or actively) for other APs in orderto transition to and associate to another AP, such as AP 20(2), for anyreason.

Existing methods in dealing with sticky clients include the serving APnot responding to a client that is identified as a sticky client, andde-authenticating the sticky client. These methods can cause disruptionin the service and still permit the client to stay with its current APat the cost of lower service quality.

Presented herein are multiple techniques to remove a sticky client. Thereason for multiple methods is that clients might have differentalgorithms for initiating a roaming process to associate to a differentAP. Some clients only evaluate the beacon from its associated AP todecide whether or not to roam, while some clients might also include thereceive signal strength indication/information (RSSI) reading that theclient generates from received unicast frames. The most efficient methodultimately depends on the roaming algorithm that is used by clientvendors. For instance, some Wi-Fi devices that use a particular Wi-Fichip-set, start a roaming process when the basic service set (BSS) islost, which can be defined as when a certain number of consecutivebeacons are missed.

Reference is now made to FIG. 2 that shows a block diagram of an AP thatis capable of performing the methods presented herein to remove a stickyclient from an AP. The AP shown in FIG. 2 is identified generally byreference numeral 20(i) and is representative of any of the APs shown inFIG. 1.

The AP 20(i) includes a baseband processor (e.g., modem) 100, aplurality of transmitters 102(1)-102(K), a plurality of receivers104(1)-104(K), a plurality of antennas 106(1)-106(K), a controller 120and a memory 130. Each transmitter 102(1)-102(K) is connected to acorresponding one of the plurality of antennas 106(1)-106(K), andlikewise each receiver 104(1)-104(K) is connected to a corresponding oneof the plurality of antennas 106(1)-106(K). The baseband processor 100includes nulling logic 110 that is used to send a transmission withnulling parameters, as described further herein. That is, the nullinglogic 110 may be used to send a transmission with antenna-weighting(spatial nulling) parameters to reduce the SNR at one or more clientdevices for signals transmitted by the AP. The baseband processor 100may be implemented by fixed or programmable digital logic gates, such asin the form of an application specific integrated circuit (ASIC), or maybe implemented by a dedicated digital signal processor, microprocessoror microcontroller. The nulling logic 110 is only one of severalfunctional blocks of the baseband processor 100, and again, it may beimplemented by digital logic gates or by instructions executed by amicroprocessor.

The controller 120 is coupled to the baseband processor 100 and provideshigher level control for the AP 20(i). The controller 120 may be amicroprocessor or microcontroller. The memory 130 stores instructionsthat the controller 120 executes to perform the control functions of theAP 20(i). Among these functions are operations performed when thecontroller 120 executes the sticky client detection and removal software140 stored in memory 130.

The memory 130 may comprise read only memory (ROM), random access memory(RAM), magnetic disk storage media devices, optical storage mediadevices, flash memory devices, electrical, optical, or otherphysical/tangible memory storage devices. Thus, in general, the memory130 may comprise one or more tangible (non-transitory) computer readablestorage media (e.g., a memory device) encoded with software comprisingcomputer executable instructions and when the software is executed (bythe controller 120) it is operable to perform the operations describedherein.

Turning now to FIG. 3, a flow chart is shown for a method 200. At 210,the AP determines that at least one particular client that is associatedto the AP should not be associated to the wireless access point, thatis, the particular client is a sticky client. There are many ways todetect/determine that a client is a “sticky” client. One technique isfor the AP to observe a weak signal from a client for a period of time.At 220, the AP transmits frames so that they are received at theparticular client device with reduced strength so as to provoke theparticular client device to transition from the AP. Several techniquesfor transmitting frames are described hereinafter in connection withFIGS. 4-11. In particular, FIGS. 4 and 5 illustrate a first method,FIGS. 8 and 9 illustrate a second method and FIGS. 10 and 11 illustratea third method. In one embodiment, the AP may start with the firstmethod, and if the client does not roam, then perform the second method,and then if the client still does not roam, then perform the thirdmethod. The third method is the most intrusive of the three methods andtherefore is performed as a last resort. However, each method on its ownhas merit as well, and thus each method may be separately performed.

As will become apparent from the following, beacons as defined in theIEEE 802.11 standard play a role in controlling whether a clientattempts to roam to a new AP because clients evaluate the receive power(RSSI) and/or the receive SNR) of beacons transmitted by its serving AP.Some clients exclusively rely on the beacon to “evaluate the AP”, andbase their behavior (roaming etc.) solely based on receivecharacteristics of beacons, while other clients use the beacon to assessthe AP presence, but may also derive their roaming or rate shiftingbehavior from additional elements, such as unicast/multicast/broadcastframes. In general, the goal of the methods presented herein is for thesticky client to receive a beacon, possibly along with other unicast,multicast, or broadcast frames, at a lower power than other clientsassociated to that AP, so that the sticky client determines the AP isfar away and therefore the sticky client attempts to transition to andassociate with another AP.

Referring now to FIGS. 4 and 5, the first method 300 is now described.For this method, the visibility of the AP's beacons is gradually reducedfor the sticky client for a period of time, and the AP eventuallydisassociates and maintains invisibility to the sticky client. At 310,AP gradually or fully nulls broadcast frames to the particular client.The nulling operation is performed by way of execution of the nullinglogic 110 of the AP (FIG. 2). As used herein the term “null” or“nulling” is meant to refer to spatially nulling achieved by applyingappropriate antenna weights to a signal to be transmitted across aplurality of antennas of the AP.

FIG. 5 shows an example in which AP 20(1) transmits beacons with nullingparameters to gradually or fully null the beacons (for a number ofbeacon intervals) towards the sticky client 40(4). The number of beaconintervals over which the gradual or full nulling is performed is basedon determining that the client effectively disassociates from the AP20(1). Further details on the nulling operation are describedhereinafter in connection with FIGS. 6 and 7. The nulling of beacons mayinclude initially transmitting beacons with nulling parameters topartially null beacons towards the particular client device andgradually adjusting the nulling parameters over time to increase nullingof beacons towards the particular client device. Partially nullingbeacons towards the particular client device may involve applyingnulling parameters (using antenna weights) that project a transmittedsignal (the beacon) on a space at a projection angle that is less than90 degrees with respect to a direction of a dominant eigenvector of theparticular client device. Gradually adjusting the nulling parameters mayinvolve adjusting the nulling parameters to increase the projectionangle towards 90 degrees with respect to a direction of the dominanteigenvector of the particular client device.

Alternatively, the nulling may involve fully nulling the beacons towardsthe particular client for the entirety of a number of beacon intervals.In other words, fully nulling may involve using nulling parameters(antenna weights) that achieve a projection angle substantially equal to90 degrees with respect to the direction of the dominant eigenvector ofthe particular client device.

At 320, the AP determines whether the particular client (the stickyclient) has disassociated from the AP. At 330, the process ends if theAP determines that the particular client has disassociated from the AP.Otherwise, at 340, if the particular client is still associated to theAP, then the AP transmits a frame to provoke the particular client todisassociate from the AP. The frame transmitted at 340 may be adisassociation frame or a de-authentication frame. In either case, whenthe client receives the frame transmitted at 340, it will no longer beassociated to the AP. Moreover, at 340, the AP may maintain invisibilityto the client. This may be achieved by not acknowledging any frame fromthe client, and not responding to any frame (including probe requests)from the client.

As an example, in a 4×4 multiple-input multiple-output (MIMO) channel,nulling can be achieved by transmitting along the weakest eigenvector ofthe 4×4 channel. When the intended recipient is a client with oneantenna, it is possible to effectively null towards the client since ithas only one eigenvector. Even if the client has two antennas, for thetransmission/reception of management and control frames only one antenna(one spatial stream, SS=1) is used and the AP performs nulling towardthat one antenna, which in fact is the same antenna for which the AP hasobtained the client's channel state information, through anacknowledgement (ACK) frame or other uplink frames transmitted by theclient.

Nulling is not location specific, rather it is more client specific.Nulling works in a radio frequency (RF) mathematical domain. It mayimpact other non-targeted clients, but statistically that impact onother clients will be minimal. Moreover, the AP can, in advance ofperforming the nulling operation, determine how correlated the RFchannels are for multiple clients. This is an attribute of theenvironment and can be determined by the AP (or re-determined asnecessary to take into account the changes in the RF environment (in agiven venue). The AP can cross-correlate the channels of a selectednumber of clients and conclude whether or not the environment is highlycorrelated by comparing the cross-correlation to a threshold value. Ifthe AP determines that the environment is highly correlated then itwould avoid performing the nulling operation and instead resort to apower-altering method, which is the second method referred to above, anddescribed hereinafter in connection with FIGS. 8 and 9.

Reference is now made to FIGS. 6 and 7 for further details on thenulling technique. The AP first obtains the RF signature or ChannelState Information (CSI) of the particular target/sticky client. The APregularly updates the CSI for purposes of updating beamforming weightsto the client, and this CSI can be used for generating nullingparameters without additional processing. The source of the CSI are theuplink frames that the client sends, such as data, management or controlframes, as described above.

For full nulling, the AP aims at the estimated CSI and nulls toward thisdirection. For partial nulling, the AP selects a vector that is notfully aligned with the estimated CSI, and has a given angle. All thevectors that fall on the surface of a cone, whose axis is the estimatedCSI vector, qualify for partial nulling. In FIG. 6, this is shown as(half-drawn) cones where the estimated CSI is the axis of the cone asshown by the vector at reference numeral 350, and the vectors with givenangles fall on the surface of the cone. FIG. 6 shows two cones. Cone 360based on a vector selected that achieves partial yet strong nullingsince it is within a closer neighborhood with respect to the estimatedCSI vector 350. Cone 370 is based a vector selected that causes partialand weaker nulling since it is farther from the estimated CSI vector350.

One with ordinary skill in the art would understand that selecting avector on the surface of a cone is mathematically equivalent to rotatingthe vector 350 by a given rotation matrix (a rotation matrix,corresponding to a set of antennas weights, that fits the dimension ofthe antenna array of the AP).

FIG. 7 shows simulation results for nulling applied according to theabove description. The antenna array is of size 4 in this simulation.For the purpose of this simulation, four-dimensional rotation matricesaccording to this reference are selected. The plots in FIG. 7 show theability of an AP to control the amount of nulling loss by the selectionof the rotation matrix.

Reference is now made to FIGS. 8 and 9 for a description of the secondmethod. FIG. 8 shows a flow chart for method 400, and FIG. 9 graphicallyillustrates this method. In this method, the AP gradually reduces powerof unicast frames to the sticky client so that the client disassociates,and then the AP becomes practically invisible to the client for a periodof time (the AP signal may still reach the client to some degree). At410, the AP gradually reduces transmit power for unicast frames destinedfor the particular client device. The time to start this phase is chosenso that there would not be many/any broadcast frames during this time.The amount of transmit power reduction is chosen so that the clientwould still acknowledge the frame, to avoid the need for the AP toretransmit several times to obtain acknowledgement. At 420, the APtransmits a frame to the particular client to cause it to disassociatefrom the AP. This frame may be a disassociation frame or ade-authentication frame, and it is sent with normal transmit power. At430, the AP transmits beacons with nulling parameters to partially orfully null the beacons towards the particular client. In one form,operations 410 and 430 may be performed in parallel (at the same time)and operation 420 performed thereafter. Method 400 targets those clientsthat use RSSI of beacons and unicast frames that are addressed to theclient for triggering roaming of the client.

Reference is now made to FIGS. 10 and 11 to describe the third method.FIG. 10 illustrates a flow chart for this method shown at referencenumeral 500. FIG. 11 graphically illustrates method 500. This method isthe most intrusive, and in general it is used as a last resort becausethe goal is for the AP to become “invisible” to the client for alltransmissions. At 510, the AP partially or fully nulls beacons towardsthe particular client. At 520, for all other non-beacon frames (unicastframes, multicast frames, beacon, broadcast frames, etc.), the AP nullsthose frames towards the particular client. At 530, the AP determineswhether the particular client has disassociated from the AP. If it did,then the method 500 ends at 540. Otherwise, at 550, the AP transmits aframe to provoke the particular client to disassociate from the AP, andmaintains invisibility from the particular client. Method 500 targetsthose clients that use RSSI of any frame that originates from theassociated AP for triggering the roaming process. The beamformingcapability of the AP becomes limited during the nulling period, howeverthis is for a relatively short period of time (several beacon periods).

The length of a nulling period used in the above methods is chosen suchthat: (a) the sticky client notices absence of the beacon of theassociated AP for T1 Target Beacon Transmission Time (TBTT) intervalsand starts a beacon search procedure, plus (b) the length of a scaninterval, T2 TBTT intervals. T1 varies for different vendors, and inthis algorithm a maximum of known T1 values is considered. T2 may bedifferent for 2.4 GHz and 5 GHz bands, if the number of scanned channelsis different.

To summarize, the techniques presented herein use nulling methods forframes to provoke the client to take an action, such as scanning otherchannels, or probing etc. In particular, beacon frames are transmittedso that they are received with lower power for several TBTT periods sothat the intended client seeks association with surrounding APs thathave a stronger signal level (RSSI) and/or received SNR (i.e., betterchannel quality) for that client.

The nulling schemes presented herein generally are intended to addressone sticky client at a time. It is unlikely that there would be severalsticky clients requiring disassociation at a given time in a BSS, andeven if there are several sticky clients, the AP would target eachsticky client, one at a time, for several Beacon intervals, and thenaddress the next sticky client.

The use of all three methods described above may be coordinated in sucha manner that AP transmits beacons with nulling parameters to null thebeacons towards the particular client device for one or more beaconintervals. If the particular client device has not transitioned from thewireless access point after one or more beacon intervals, then unicastframes destined for the particular client device are transmitted withgradually reduced power over a period of time. If the particular clientdevice has not transitioned from the wireless access point after theperiod of time, then all non-beacon frames, which are not addressed tothe particular client device, are transmitted with nulling parameters tonull the non-beacon frames towards the particular client device.

In summary, in one form, a method is provided comprising: at a wirelessaccess point that serves one or more wireless client devices in awireless network: determining that at least one particular client devicethat is associated to the wireless access point should not be associatedto the wireless access point; and transmitting frames so that they arereceived at the particular client device with reduced strength so as toprovoke the particular client device to transition from the wirelessaccess point.

In another form, a wireless access point is provided comprising: aplurality of transmitters, each associated with a corresponding one of aplurality of antennas; a plurality of receivers, each associated with acorresponding one of the plurality of antennas; and a baseband processorcoupled to the plurality of transmitters and the plurality of receivers,wherein the baseband processor: determines that a particular clientdevice that is associated to the wireless access point should not beassociated to the wireless access point; and causes frames to betransmitted via the plurality of antennas so that they are received atthe particular client device with reduced strength so as to provoke theparticular client device to transition from the wireless access point.

Further, non-transitory computer readable storage media encoded withinstructions that, when executed by a processor, cause the processor toperform operations for a wireless access point that serves one or morewireless client devices in a wireless network, the operationscomprising: determining that at least one particular client device thatis associated to the wireless access point should not be associated tothe wireless access point; and causing frames to be transmitted so thatthey are received at the particular client device with reduced strengthso as to provoke the particular client device to transition from thewireless access point.

The above description is intended by way of example only. Variousmodifications and structural changes may be made therein withoutdeparting from the scope of the concepts described herein and within thescope and range of equivalents of the claims.

What is claimed is:
 1. A method comprising: at a wireless access pointthat serves one or more wireless client devices in a wireless network:determining that at least one particular client device that isassociated to the wireless access point should not be associated to thewireless access point; and transmitting frames so that they are receivedat the particular client device with reduced strength so as to provokethe particular client device to transition from the wireless accesspoint.
 2. The method of claim 1, wherein transmitting comprisestransmitting beacons with nulling parameters to null the beacons towardsthe particular client device for one or more beacon intervals.
 3. Themethod of claim 2, wherein transmitting beacons with nulling parameterscomprises initially transmitting beacons with spatial nulling parametersto partially null beacons towards the particular client device andgradually adjusting the nulling parameters over time to increase nullingof beacons towards the particular client device.
 4. The method of claim2, further comprising: determining whether the particular client devicehas transitioned from the wireless access point; if it is determinedthat the particular client device has not transitioned from the wirelessaccess point, transmitting a frame to the particular client device toprovoke the particular client device to disassociate from the wirelessaccess point.
 5. The method of claim 2, wherein transmitting comprises:transmitting all non-beacon frames, which are not addressed to theparticular client device, with nulling parameters to null the non-beaconframes towards the particular client device.
 6. The method of claim 5,if it is determined that the particular client device has nottransitioned from the wireless access point, transmitting a frame to theparticular client device to provoke the particular client device todisassociate from the wireless access point.
 7. The method of claim 1,wherein transmitting comprises: transmitting unicast frames destined forthe particular client device with gradually reduced power over a periodof time; transmitting beacons with nulling parameters to null thebeacons towards the particular client device; and transmitting a frameto the particular client device to provoke the particular client deviceto disassociate with the wireless access point.
 8. The method of claim7, wherein the transmitting the frame to provoke the particular clientdevice to disassociate is performed after transmitting unicast frames tothe particular client device with gradually reduced power over a periodof time, and wherein transmitting beacons with nulling parameters isperformed after transmitting the frame to provoke the particular clientdevice to disassociate.
 9. The method of claim 7, wherein thetransmitting unicast frames with gradually reduced power and thetransmitting beacons with nulling parameters to the particular clientdevice are performed in parallel for a period of time, and thetransmitting the frame to provoke the particular client device todisassociate is performed after the period of time.
 10. The method ofclaim 7, further comprising determining a time to initiate graduallyreducing power for unicast frames so that there are few or no broadcastframes while unicast frames are transmitted with reduced power to theparticular client device.
 11. The method of claim 1, where transmittingcomprises: transmitting beacons with nulling parameters to null thebeacons towards the particular client device; if the particular clientdevice has not transitioned from the wireless access point after one ormore beacon intervals, then transmitting unicast frames destined for theparticular client device with gradually reduced power over a period oftime; and if the particular client device has not transitioned from thewireless access point after the period of time, then transmitting allnon-beacon frames, which are not addressed to the particular clientdevice, with nulling parameters to null the non-beacon frames towards tothe particular client device.
 12. A wireless access point comprising: aplurality of transmitters, each associated with a corresponding one of aplurality of antennas; a plurality of receivers, each associated with acorresponding one of the plurality of antennas; and a baseband processorcoupled to the plurality of transmitters and the plurality of receivers,wherein the baseband processor: determines that a particular clientdevice that is associated to the wireless access point should not beassociated to the wireless access point; and causes frames to betransmitted via the plurality of antennas so that they are received atthe particular client device with reduced strength so as to provoke theparticular client device to transition from the wireless access point.13. The wireless access point of claim 12, wherein if it is determinedthat the particular client device has not transitioned from the wirelessaccess point, the baseband processor transmits a frame to the particularclient device to provoke the particular client device to disassociatefrom the wireless access point.
 14. The wireless access point of claim12, wherein the baseband processor causes beacons to be transmitted withnulling parameters to null the beacons towards the particular clientdevice for one or more beacon intervals.
 15. The wireless access pointof claim 14, wherein the baseband processor causes beacons to beinitially transmitted with nulling parameters to partially null beaconstowards the particular client device and gradually adjusts the nullingparameters over time to increase nulling of beacons towards theparticular client device.
 16. The wireless access point of claim 14,wherein the baseband processor causes all non-beacon frames, which arenot addressed to the particular client device, to be transmitted withnulling parameters to null the non-beacon frames towards the particularclient device.
 17. The wireless access point of claim 12, wherein thebaseband processor: causes unicast frames destined for the particularclient device to be transmitted with gradually reduced power over aperiod of time; and causes beacons to be transmitted with nullingparameters to null the beacons towards the particular client device. 18.The wireless access point of claim 12, wherein the baseband processor:causes beacons to be transmitted with nulling parameters to null thebeacons towards the particular client device; if the particular clientdevice has not transitioned from the wireless access point after one ormore beacon intervals, causes unicast frames destined for the particularclient device to be transmitted with gradually reduced power over aperiod of time; and if the particular client device has not transitionedfrom the wireless access point after the period of time, causes allnon-beacon frames, which are not addressed to the particular clientdevice, to be transmitted with nulling parameters to null the non-beaconframes towards to the particular client device.
 19. A non-transitorycomputer readable storage media encoded with instructions that, whenexecuted by a processor, cause the processor to perform operations for awireless access point that serves one or more wireless client devices ina wireless network, the operations comprising: determining that at leastone particular client device that is associated to the wireless accesspoint should not be associated to the wireless access point; and causingframes to be transmitted so that they are received at the particularclient device with reduced strength so as to provoke the particularclient device to transition from the wireless access point.
 20. Thenon-transitory computer readable storage media of claim 19, wherein theinstructions for causing frames to be transmitted comprise instructionsthat cause beacons to be transmitted with nulling parameters to null thebeacons towards the particular client device.
 21. The non-transitorycomputer readable storage media of claim 19, wherein the instructionsfor causing frames to be transmitted comprise instructions that causebeacons to be initially transmitted with nulling parameters to partiallynull beacons towards the particular client device and to graduallyadjust the nulling parameters over time to increase nulling of beaconstowards the particular client device.
 22. The non-transitory computerreadable storage media of claim 19, wherein the instructions for causingframes to be transmitted comprise instructions that cause all non-beaconframes, which are not addressed to the particular client device, to betransmitted with nulling parameters to null the non-beacon framestowards the particular client device.
 23. The non-transitory computerreadable storage media of claim 19, wherein the instructions for causingframes to be transmitted comprise instructions that: cause unicastframes destined for the particular client device to be transmitted withgradually reduced power over a period of time; and cause beacons to betransmitted with nulling parameters to null the beacons towards theparticular client device.
 24. The non-transitory computer readablestorage media of claim 19, wherein the instructions for causing framesto be transmitted comprise instructions that: cause beacons to betransmitted with nulling parameters to null the beacons towards theparticular client device; if the particular client device has nottransitioned from the wireless access point after the one or more beaconintervals, cause unicast frames destined for the particular clientdevice to be transmitted with gradually reduced power over a period oftime; and if the particular client device has not transitioned from thewireless access point after the period of time, cause all non-beaconframes, which are not addressed to the particular client device, to betransmitted with nulling parameters to null the non-beacon framestowards to the particular client device.